Liquid air method and apparatus

ABSTRACT

A method and apparatus in which air is liquefied and stored for later energy recovery during which the liquid air is pumped to high pressure, heated and then expanded to recover the energy. During the recovery of energy, the pumped liquid air is heated within a regenerator that stores the refrigeration within the liquid air. During the liquefaction of the air, part of the refrigeration required is obtained from the refrigeration stored in the regenerator.

RELATED APPLICATIONS

This application is a utility application of provisional application Ser. No. 61/266,347, filed Dec. 3, 2009.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus in which air is liquefied and stored for later energy recovery during which the liquid air is pumped to high pressure, heated and then expanded to recover the energy, with possible multiple expansions and reheat between expansions. More particularly, the present invention relates to such a method and apparatus that employs an integrated liquefier-regenerator system in which part of the refrigeration for a liquefier, used in liquefying the air, is provided by a regenerator that stores refrigeration imparted to the regenerator during the heating of the pumped and pressurized air.

BACKGROUND

The electric grid is in place to connect and balance electric generation and consumption. Due to the instantaneous variations in consumption and generation and the corresponding mismatch between them, the grid needs to include means of storing energy during periods of oversupply, and redeploy it during period of over demand. Due to an increase of non dispatchable generation sources, the mismatch between electricity supply and demand has been growing in the last few years, and it is poised to reach levels that could compromise the stability of the grid. In order to avoid such outcome, an increased amount of energy storage is necessary.

In the prior art, it has been proposed to store energy by liquefying air during periods of oversupply and then recovering the energy during periods of demand by vaporizing the liquid air and recovering the energy by expanding the air after having been vaporized. As will be discussed, among other advantages, the present invention stores refrigeration within a regenerator during the vaporization of the air that is later recovered and used to supply part of the refrigeration requirements in liquefying the air. This integration between the liquefier and the regenerator reduces the energy required in the liquefaction of the air.

SUMMARY OF THE INVENTION

The present invention, in one aspect, provides a liquid air storage and energy recovery method. In accordance with such method, during an energy recovery phase, energy is recovered from liquid air stored in a storage tank by pumping a stream of the liquid air to produce a pumped air stream, passing the pumped air stream through a regenerator such that refrigeration contained in the pumped air stream is stored within the regenerator and the pumped air stream warms within the regenerator to produce a pressurized air stream. The pressurized air stream is expanded to produce power. During a liquid air storage phase, air is liquefied to produce a liquid air stream. The liquid air stream is introduced into the storage tank to produce the liquid air stored in the storage tank. Part of the refrigeration requirement for liquefying the air is provided with the refrigeration stored in the regenerator and another part of refrigeration is provided by means of a liquefier.

An air stream can be compressed to produce a compressed air stream. A first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part by dividing the compressed air stream into two portions. The first subsidiary stream is introduced into the liquefier to produce a first cooled, high pressure air stream and the second subsidiary stream is introduced into the regenerator to produce a second cooled, high pressure air stream. A vapor phase stream indirectly exchanges heat with the second cooled high pressure air stream to further cool the second cooled high pressure air stream. The first and second high pressure air streams are expanded and introduced into a phase separator to produce a liquid phase and a vapor phase. The vapor phase stream is composed of the vapor phase and after the indirect exchange of the heat with the second high cooled high pressure air stream, the vapor phase stream is introduced into the liquefier and indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream. The liquid air stream is composed of the liquid phase and is expanded to a lower pressure and then introduced into the storage tank. As a result, the part of the refrigeration requirement for liquefying the air is provided by cooling the second subsidiary stream within the regenerator, indirectly exchanging heat from the second high pressure air stream to the vapor phase stream and the indirect heat exchange of the vapor phase stream within the liquefier.

The air stream can be compressed in a feed compressor along with a first recycle stream to form a first combined stream. The first combined stream is compressed in a recycle compressor along with a second recycle stream to form a second combined stream. The second combined stream is divided into the first subsidiary stream and the second subsidiary stream. The first subsidiary stream is expanded at two temperature levels within the liquefier to generate first and second exhaust streams that indirectly exchange heat with the air cooling within the liquefier. The first exhaust stream results from expansion at a lower of the two temperature levels and the second exhaust stream results from expansion at a higher of the two levels. The first exhaust stream forms the first recycle stream after having been fully warmed within the liquefier and the second exhaust stream forms the second recycle stream after having been fully warmed within the liquefier. The vapor phase stream after, having exchanged heat with the air cooling within the liquefier, can be recycled back to the inlet of the feed compressor.

The pressurized air stream can be heated in a heat recuperator. In such case, the pressurized air stream is expanded in at least two expanders, serially connected, with re-heat within the heat recuperator between the at least two expanders. A high temperature exhaust stream is produced as a result of the expansion of the pressurized air stream. The first combined stream is purified within a pre-purification unit and the adsorbent within the pre-purification unit is regenerated with the high temperature exhaust stream.

The pressurized air stream can be heated within a recuperator to form a heated stream that is expanded in a first expander to produce a first exhaust stream. The first exhaust stream is introduced into a combustor to produce a flue gas stream and the flue gas stream is expanded in a second expander operating at a higher temperature than the first expander to produce a second exhaust stream. The second exhaust stream is introduced into the recuperator to heat the pressurized air stream.

An air stream can be compressed to produce a compressed air stream. A first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part by dividing the compressed air stream into two portions. The first subsidiary stream is introduced into the liquefier to produce a first cooled high pressure air stream and the second subsidiary stream is introduced into the regenerator to produce a second cooled high pressure air stream. The first subsidiary air stream and the second subsidiary air stream are expanded and introduced into a phase separator to produce a liquid phase and a vapor phase. A vapor phase stream composed of the vapor phase is introduced into the liquefier and indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream and the liquid air stream, which is composed of the liquid phase, is expanded to a lower pressure and introduced into the storage tank. As a result, the part of the refrigeration requirement for liquefying the air is provided by liquefying the second subsidiary stream within the regenerator and the indirect heat exchange of the vapor phase stream within the liquefier.

In any embodiment of the present invention, the vapor phase stream can indirectly exchange heat with the first cooled high pressure air stream and the second cooled high pressure air stream to subcool the first and second cooled high pressure air stream. Additionally, in any embodiment, the pressurized air stream can be expanded by introducing the pressurized air stream into a combustor and expanding resulting flue gases in an expander. Also, at least air that is introduced into the liquefier is purified of higher boiling contaminants comprising hydrocarbons, carbon dioxide and water vapor.

The air stream can be compressed to a supercritical pressure and the stream of the liquid air can be pumped to a supercritical pressure.

In another aspect, the present invention provides a regenerator comprising two or more pipe bundles. The pipe bundles are connected to each other through one or more conduits with a higher thermal resistance than the thermal resistance of each bundle as a whole so that heat will not be conducted through the one or more conduits between bundles. The pipe bundles are located within a thermal storage medium. The thermal storage medium can be water, and the pipe bundles are submerged within a pool of the water either in solid or liquid form. Alternatively, each pipe bundle can be embedded in a thermal storage medium and the thermal storage medium is composed of a mixture of substances that will change phase during the storage and production phases. In a further alternative, the thermal storage medium is cement, gravel, ceramic, or a mineral matrix.

In yet another aspect, the present invention provides a liquid air storage and energy recovery apparatus. In such aspect of the present invention, a storage tank is provided for storing liquid air. A pump is connected to the storage tank to pump a stream of the liquid air during an energy recovery phase of operation, thereby to produce a pumped liquid air stream. A regenerator, connected to the pump, is configured such that refrigeration contained in the pumped liquid air stream is stored within the regenerator and the pumped liquid air stream vaporizes within the regenerator to produce a pressurized air stream. At least one expansion device is connected to the regenerator and is configured to expand the pressurized air stream and thereby to produce power. A liquefier is integrated with the regenerator such that during a liquid air storage phase, an air stream is liquefied to produce a liquid air stream through the refrigeration stored in the regenerator. During the energy recovery phase, additional refrigeration produced by the liquefier and the storage tank is in flow communication with the liquefier and the regenerator such that the liquid air stream is introduced into the storage tank to produce the liquid air stored in the storage tank.

At least one compressor can be provided to compress an air stream and thereby to produce a compressed air stream. The liquefier and the regenerator are in flow communication with the at least one compressor such that a first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part from the compressed air stream. The first subsidiary compressed stream is introduced into the liquefier to produce a first cooled high pressure air stream and the second subsidiary stream is introduced into the regenerator to produce a second cooled high pressure air stream. A phase separator can also be provided. Two expansion valves are positioned between the regenerator and the liquefier and the phase separator such that the first cooled high pressure air stream and the second cooled high pressure air stream are expanded and introduced into the phase separator to produce a liquid phase and a vapor phase. A heat exchanger is positioned between the phase separator and the liquefier such that a vapor phase stream composed of the vapor phase indirectly exchanges heat with the second cooled high pressure air stream to subcool the second cooled high pressure air stream and the vapor phase stream is introduced into the liquefier. The liquefier is configured such that the vapor phase stream indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream. The storage tank is in flow communication with the phase separator and another expansion valve, positioned between the phase separator and the storage tank, such that a liquid air stream, composed of the liquid phase, is expanded to a lower pressure and introduced into the storage tank. As a result, the part of the refrigeration requirement for liquefying the air is provided by liquefying the second subsidiary stream within the regenerator, indirectly exchanging heat from the second cooled high pressure air stream to the vapor phase stream and the indirectly heat exchange of the vapor phase stream within the liquefier.

The at least one compressor can comprise a feed compressor and a recycle compressor. The feed compressor compresses the air stream along with a first recycle stream to form a first combined stream and the recycle compressor is connected to the feed compressor such that the first combined stream is compressed along with a second recycle stream to form a second combined stream. The liquefier and the regenerator are connected to the recycle compressor so that the second combined stream is divided into the first subsidiary stream and the second subsidiary stream. The liquefier has two expanders positioned at two temperatures levels within the liquefier such that the first subsidiary stream is expanded at two temperature levels within the liquefier to generate first and second exhaust streams. The first exhaust stream results from expansion at a lower of the two temperature levels and the second exhaust stream results from expansion at a higher of the two levels. A heat exchange network is positioned within the liquefier such that the first and second exhaust streams indirectly exchange heat with the air cooling within the liquefier. The feed compressor is connected to the liquefier so that the first exhaust stream forms the first recycle stream after having been fully warmed within the liquefier. The recycle compressor is connected to the liquefier so that second exhaust stream forms the second recycle stream after having been fully warmed within the liquefier. The liquefier can be connected to the feed compressor such that the vapor phase stream is recycled back to the inlet of the feed compressor.

The at least one expansion device can comprise at least two expanders, serially connected, to expand the pressurized air stream and a heat recuperator can be positioned between the at least two expanders to reheat the pressurized air stream. The at least two expanders can produce a heated exhaust stream. A pre-purification unit having an adsorbent purifies air of contaminants and the pre-purification unit is positioned between the feed compressor and the recycle compressor so that the first combined stream is purified within the pre-purification unit. The pre-purification unit is connected to the at least two expanders to receive a part of the heated exhaust stream to regenerate the adsorbent contained within the pre-purification unit.

The at least one expansion device can be a first expander and a second expander. A recuperator can be provided to heat the pressurized air stream and thereby to form a heated stream. A first expander is connected to the recuperator to expand the heated stream and thereby to produce a first exhaust stream and a combustor connected to the first expander to expand the first exhaust stream and thereby to produce a flue gas stream. A second expander is connected to the combustor to expand the flue gas stream at a higher temperature than the first expander to produce a second exhaust stream. The recuperator is also connected to the second expander so that the second exhaust stream is introduced into the recuperator to heat the pressurized air stream.

At least one compressor can be provided to compress an air stream and thereby to produce a compressed air stream. The liquefier and the regenerator are in flow communication with the at least one compressor such that a first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part from the compressed air stream. The first subsidiary compressed stream is introduced into the liquefier to produce a first cooled high pressure air stream and the second subsidiary stream is introduced into the regenerator to produce a second cooled high pressure air stream. A phase separator can be provided and two expansion valves can be positioned between the regenerator and the liquefier such that the first cooled high pressure air stream and the second cooled high pressure air stream are expanded and introduced into the phase separator to produce a liquid phase and a vapor phase. The liquefier is connected to the phase separator and is configured such that a vapor phase stream composed of the vapor phase indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream. The storage tank is in flow communication with the phase separator and another expansion valve is positioned between the phase separator and the storage tank such that a liquid air stream, composed of the liquid phase, is expanded to a lower pressure and introduced into the storage tank. The liquid air stream is composed of the liquid phase and is expanded to a lower pressure and then introduced into the storage tank. As a result, the part of the refrigeration requirement for liquefying the air is provided by liquefying the second subsidiary stream within the regenerator and the indirect heat exchange of the vapor phase stream within the liquefier.

The heat exchanger used in subcooling the second cooled high pressure air stream can also be configured such that the vapor phase stream also indirectly exchanges heat with the first cooled high pressure air stream to subcool the first cooled high pressure air stream.

A combustor can be positioned between the at least one expansion device and the regenerator such that the pressurized air stream supports combustion within the combustor to generate a flue gas stream and the flue gas stream is expanded within the at least one expansion device.

The at least one compressor can have subsequent stages of compression and purification units containing molecular sieve adsorbent can be located between the stages of compression to purify the air during compression. A pre-purification unit containing molecular sieve adsorbent can be connected to the at least one compressor so that at least part of the compressed air is purified within the pre-purification unit.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims distinctly pointing out the subject matter that Applicants regard as their invention, it is believed that the present invention will be better understood when taken in connection with the accompanying drawings in which:

FIG. 1 illustrates a schematic diagram of the liquid air storage and energy generation apparatus;

FIG. 2 illustrates a liquefier 20 used in FIG. 1 operating during the storage phase;

FIG. 3 is a fragmentary view alternative embodiment of FIG. 1;

FIG. 4 illustrates a regenerator used in connection with FIG. 1

FIG. 5 illustrates a fragmentary view of an alternative embodiment of the present invention illustrating an arrangement of expanders that could be used in the apparatus shown in FIG. 1. FIG. 1; and

FIG. 6 is an alternative embodiment of FIG. 4.

DETAILED DESCRIPTION

With reference to FIG. 1, an apparatus 1 is illustrated for liquefying air contained in a feed air stream 10 and thereafter, extracting energy from the liquid air that can be applied for the production of electrical power. Briefly, apparatus 1 is designed to operate in two phases, namely, a liquid air storage phase and an energy recovery phase.

During the liquid air storage phase, feed air stream 10 is compressed within a feed compressor 12 and optionally, a recycle compressor 14 and then divided into a first subsidiary compressed stream 16 and a second subsidiary compressed stream 18. Part of the refrigeration requirement for liquefying the air is provided by a liquefier 20 and a regenerator 22 in which refrigeration has been previously stored during the energy recovery phase. In the embodiment of the present invention illustrated in FIG. 1, this is done by passing the first subsidiary compress stream 16 into a liquefier 20 and the second subsidiary stream into the regenerator 22 to produce a first cooled high pressure air stream 24 and a second cooled high pressure air stream 26, respectively. The first cooled high pressure air stream 24 and the second cooled high pressure air stream 26 are then valve expanded in expansion valves 27 and 28, respectively, to produce two phase streams and introduced into a phase separator 29 where resulting vapor and liquid phases are disengaged. A liquid phase stream 30 is then expanded to a lower pressure by an expansion valve 31 and stored within a storage tank 32 thereby completing the liquid storage phase.

During the energy recovery phase, a liquid air stream 34 is extracted from the storage tank 32, is pumped within a pump 36 to produce a pumped air stream 38. The pumped air stream 38 is then warmed within the regenerator 22, thereby storing refrigeration for the subsequent liquid storage phase to produce a high pressure air stream 40 that is subsequently expanded within expanders 118 and 124 from which the energy of expansion can be extracted by a generator.

Having briefly described an embodiment for carrying out the present invention, a more detailed description begins with the compression of feed air stream 10. Feed air stream 10 and optionally, an intermediate pressure air stream 42 that has been purified and recycle streams 44 and 45, produced in the liquefier 20, are compressed to an intermediate pressure in a compressor 12. The resulting intermediate compressed air is withdrawn from an intermediate state of compressor 12, cooled in an aftercooler 46 and purified in a pre-purification unit 48. Pre-purification unit 48 as known in the art can contain one or more types of molecular sieves that adsorb such higher boiling components of the air as carbon dioxide, water vapor and hydrocarbons such as carbon monoxide. The resulting intermediate pressure air stream 42 that has been purified of the higher boiling contaminants is then recirculated back to the compressor 12 along with recycle stream 44. The pre-purification unit 48 can be of the type in which an adsorbent bed is utilized that is not regenerated or consists of multiple beds operating in an out-of-phase cycle, such as a temperature or pressure swing cycle or a combination of such cycles, that allows for regeneration of the beds.

As can be appreciated, there are other options for purifying the air, for example, using adsorbents to purify the air upstream of the apparatus 1. Additionally, the air can be pre-purified after the air has been compressed to the pressure at which the liquefier 20 or regenerator 22 are operated. Another possibility is to use a portion or all of a recycle stream 55 (to be discussed) to regenerate adsorbent beds containing within the pre-purification unit 48. A further alternative to achieve satisfactory air purification is to purify only the air that is directed toward the liquefier 20. The moisture and carbon dioxide air directed toward the regenerator 22 will freeze in the regenerator passages, but since less air travels through the regenerator 22 during the storage phase than during the power producing phase, these contaminants will be removed during the latter phase. If there is a lack of driving force to remove the contaminants, some dry air or nitrogen at a temperature higher than the evaporation or sublimation temperature of said contaminants can be passed through the regenerator 22.

The air that is fully compressed in compressor 12 is discharged therefrom as a compressed air stream 50 that can constitute a combined stream given the optional recycle of recycle streams 44 and/or 45. Compressed air stream 50, after passage through an aftercooler 52, is then compressed further in the recycle compressor 14 up to supercritical pressure, cooled in an aftercooler 54 and then split into at least two portions that consist of the first subsidiary compressed stream 16 directed toward the liquefier 20 and the second subsidiary compressed stream 18 directed toward the regenerator 22. It is to be noted that both compressor 12 and recycle compressor 14 can be multi-stage, intercooled machines in which the stages are commonly driven by a bull gear driving driven gears connected to the compression stages. One or more adiabatic compressors can be utilized in place of multistage inter-cooled compressors, and recuperate the heat of compression either by storing it in a regenerator or by using it to run one or more absorption chillers. Although not illustrated, an air suction filter house could be provided upstream of the compressor 12 for filtering the incoming air. The compressed air produced by the recycle compressor 14 can be another combined stream if an optional recycle stream 55, also produced in the liquefier 20, is introduced into an intermediate compression stage of recycle compressor 14 and compressed along with compressed air stream 50.

The air exits from the cold end of the liquefier 20 as the first cooled high pressure air stream 24 that is expanded in valve 27 to a pressure higher than atmospheric and sent to the phase separator 29. The second subsidiary compressed stream 18 exits the regenerator 22 as the second cooled high pressure air stream 26 that is further cooled in a subcooler 56 and expanded in valve 28 to a pressure higher than atmospheric and sent to the phase separator 29. The phase separator 29 directs the liquid phase stream 30, composed of the liquid phase, toward the storage tank 32, throttling it through a valve 31, while a vapor phase stream 58 composed of the gaseous phase is optionally directed back to the subcooler 56 to recover part of the refrigeration of such stream by subcooling the second cooled high pressure air stream 26 within the subcooler 56 and to indirectly exchange heat with the air cooling within the liquefier 20 that forms the first cooled high pressure air stream 24. Thus, as briefly discussed above, part of the refrigeration requirement for liquefying the air is provided by cooling the second subsidiary compressed stream 18 within the regenerator 22, indirectly exchanging heat from vapor phase stream 58 to the second cooled high pressure air stream 26 within subcooler 56 and the indirect heat exchange of the vapor phase stream 58 with the air being cooled within the liquefier 20. This is of course advantageous in that the refrigeration of the vapor phase stream 58 is recovered to decrease the power requirements involved in the liquefaction of the air.

The phase separator 29 should be operated at a pressure as low as possible, but high enough to drive the gaseous phase through the liquefier passages. The vapor phase stream 58 originating in the phase separator 29, after warming within the liquefier 20, is optionally redirected to the inlet of the compressor 12 as the recycle stream 45 to prevent oxygen enrichment of the liquid air in the storage tank 32. In this regard, oxygen enrichment in the storage tank 32 can also be prevented by monitoring the oxygen concentration and supplying nitrogen as needed from a separate liquid nitrogen tank. However, it is possible to vent recycle stream 45 as shown in FIG. 3, discussed in more detail below. It is also possible to use at least part of such stream in regenerating adsorbents utilized in pre-purification unit 48.

A more detailed schematic of the liquefier 20 is shown in FIG. 2. Liquefier 20 is provided with a heat exchanger 60 that can be a system of heat exchange sections having a warm temperature heat exchange section 62, an intermediate temperature heat exchange section 64 and a cold end temperature heat exchange section 66. Although the heat exchange sections are illustrated as being separated, in fact, they could be integrated in a single heat exchanger of brazed aluminum plate-fin construction. Also provided is a warm expander 68 and one or more cold expanders, preferably cold expanders 70 and 72. The warm and cold expanders 68, 70 and 72 are preferably connected by a gear box 74 to commonly drive an electrical generator 76 that can be used to help power the compressors 12 and 14.

As indicated above, the air coming from the aftercooler 54 is split into the first and second subsidiary compressed streams 16 and 18. The first subsidiary compressed stream 16 is in turn further divided into streams 16 a and 16 b. Stream 16 a directed toward the liquefier 20 and is sent through the warm heat exchange section 62 and intermediate temperature heat exchange section 64, while the stream 16 b is first expanded through a warm turbine 68 and then sent as exhaust stream 78 to the warm heat exchange section 62 in counterflow with stream 16 a. Exhaust stream 78 exits the warm heat exchange section 62 as recycle stream 55. Stream 16 a after passage through the intermediate heat exchange section 64 is divided into streams 16 c and 16 d. Stream 16 c forms the first cooled high pressure air stream 24 after having been discharged from the cold heat exchange section 66. Stream 16 d is expanded through the cold turbines 70 and 72 to a pressure of roughly 100 psia to form exhaust stream 82 that in turn, after having been fully warmed within the heat exchanger 60, is discharged as the recycle stream 44. Vapor phase stream 58 from the phase separator 29 flows through the heat exchanger 60 and is discharged from the warm heat exchange section 62 as the recycle stream 45 that is sent back to the inlet of the compressor 12. As a result, part of the refrigeration needed to sustain the operation of the liquefier 20 is provided by the flash-off gases as vapor phase stream 58 and thus, in such manner, there exists a thermal integration between the liquefier 20 and the regenerator 22.

The amount of air withdrawn to feed each of the turbines 68, 70 and 72 can be adjusted to optimize the thermal profiles in the heat exchanger 60. The expansion pressure and expansion ratio of each of the turbines 68, 70 and 72 can also be adjusted to reach an optimum between thermal efficiency in the liquefier's heat exchangers and compression efficiency in the compression stages.

It is to be noted that there are many other possible embodiments of the present invention involving the integration of the liquefier into the apparatus 1 and its use with phase separators feeding a liquid storage tank. For example, the air exiting the liquefier 20, or the air exiting the regenerator 22, or both could be expanded using one or more turbines, followed by one or more valves capable of throttling the expanded air to the pressure at which the phase separator 29 is operated. In this regard, more than one phase separator could be used in place of phase separator 29, allowing the air coming from the liquefier 20 and the air coming from the regenerator 22 to be expanded to two different pressures, hence generating two vapor phase streams with different properties. The operating pressures could be optimized to provide the right amount of refrigeration at the right temperature inside the liquefier 20. If more than one phase separator were used, different vapor phase streams could enter the liquefier 20 at different locations, in order to reach an optimal temperature profile along the liquefier heat exchanger sections. The liquefier 20 can be designed to use one or more turbines, placed at different points in the heat exchanger 60. Furthermore, the turbines illustrated in liquefier 20 could be replaced by Joule-Thompson valves. The streams leaving the liquefier 20 can be either vented or recompressed to any suitable level. The flash-off resulting from the pressure reduction between the phase separator 29 and the storage tank 32 can be used to do any combination of the following: cool the regenerator, cool any of the streams entering or exiting the phase separator, or enter a separate passage in the liquefier to provide additional refrigeration to one or more sections of the heat exchanger. Any recycle stream composed of dry low pressure dry gas exiting the liquefier 20 could be introduced into a booster compressor to raise their pressure above the outlet pressure of the pre-purification unit 48, and integrate them in the first stage of compressor 12 following the pre-purification unit 48. Further, any low pressure dry gas exiting the liquefier 20 could be introduced into an appropriate stage of compression before the pre-purification unit 48.

The streams leaving the liquefier 20 and being directed to a specific stage of compression can be either compressed or expanded prior to entering said stage of compression. The expansion can take place either through a valve or through a turbine. In order to enhance the operational flexibility of the system, the liquefier 20 can be sized in excess of what is needed to close the heat balance of the system. The excess capacity of the liquefier will allow the system to produce more air than the design quantity, so that the expansion cycle can be run for a longer period of time when needed.

With additional reference to FIG. 3, recycle stream 55 is vented. In fact in any embodiment of the present invention, recycle stream 55 could be vented. Additionally, a subcooler 56′ is employed that is used to subcool both the first cooled high pressure air stream 16 and the second cooled high pressure air stream 18 through indirect heat exchange with the vapor phase stream 58. Each or both of these features could be employed in any embodiments. Conversely, possible embodiments of the present invention might be constructed without either subcooler 56 or 56′.

Regenerator 22 can be designed to provide from 20% to 99% of the refrigeration necessary to complete a full storage and deployment cycle. With reference to FIG. 4, the regenerator 22 is preferably formed of a number of pipe bundles 100, each having a plurality of pipes 102 connected at opposite ends to manifolds 104 in a matrix that is located within a thermal storage medium 106 that can be a pool of water. The pipe bundles 100 are connected by connection conduits 108. The second subsidiary compressed stream 18 is introduced into an end conduit 110 and the second subsidiary compressed stream 18 flows through the pipe bundles 100 by way of the connection conduits 108 and is discharged from an end conduit 112 located opposite side of regenerator 22. The water will solidify during the startup process. The water will provide the thermal ballast for the regenerator 22, and during normal operation a thermal profile will be established such that the warm end of the ice block is slightly below the freezing temperature, while the cold end is at cryogenic temperature. The thermal storage medium could be a mixture of substances that would change phase with the change in temperature during storage and production phases. Optionally, the thermal storage medium could be a mixture of water and salt, hydrocarbons and an industrial gas such as nitrogen. Also possible is a mixture of water and sand or other substances such as cement, gravel, ceramics or a mineral matrix. In order to recuperate the refrigeration at a temperature higher than the freezing point, a few pipe bundles 100 at the warm end of the regenerator 22 could be embedded in concrete, which will act as the thermal ballast in lieu of the water. The cold end of the regenerator 22 and a few pipe bundles 100 thereof would be submerged in ice. Since the connection conduits are as illustrated single pipes, such pipes will provide a high thermal resistance to heat transfer between the pipe bundles 100.

The proposed configuration has a number of advantages, among which standardization (e.g. the same bundles 100 can be used for systems of any size by adjusting their number to provide the required thermal capacity), possibility of being produced in a shop and shipped on-site inexpensively, and ability of providing bottlenecks in the thermal links between zones of the regenerator operating at different temperatures. The regenerator can be housed either in a pit dug in the ground and properly insulated or in an off-ground pool. The choice will depend on the specific conditions at the site.

An alternative to the water/cement flooded regenerator is a regenerator which employs only cement as thermal ballast. A further alternative is a regenerator that employs only water as thermal ballast, where the section at a temperature higher than freezing is separated from the permanently iced one and it is allowed to undergo phase change during every cycle.

The appropriate split between the first and second subsidiary compressed streams 16 and 18 can be determined as follows: design the regenerator 22 to provide a given thermal efficiency; calculate how much liquid air could be produced flowing high pressure air through the regenerator 22 when the latter has been cooled by the vaporization of a full charge of liquid air; size the liquefier 20 to make up the additional refrigeration needed to sustain the cyclical operation of the entire system, plus a capacity margin to allow for operational flexibility. The actual split will depend on techno-economic considerations that are quite site specific, since the relative importance of cycle efficiency over capital cost is dictated by the spread in low-to-high energy prices. It is to be noted that the capacity margin for the liquefier 20 allows more liquid air to be produced and stored in storage tank 32 at various times to increase the power that is produced by the system.

During the liquid storage phase the system will be controlled through the measurement of the flow and/or temperature of the recycle stream 45, produced by warming vapor phase stream 58 within liquefier 20 and recycled back to the feed compressor 12, aiming for its temperature to be close to ambient, but preventing temperature pinch points in the liquefier core, and regulated through the appropriate split between the first and second subsidiary compressed streams 16 and 18.

With continued reference to FIG. 1, during the power production phase, the high pressure air stream 40 is introduced into a recuperator 114 to produce a heated stream 116 that is subsequently expanded in expander 118 to produce power. The exhaust stream 120 of expander 118 is then reheated within recuperator 114 to produce a reheated stream 122 that is subsequently expanded in an expander 124 to produce an exhaust stream 126 that can be vented.

There are other possible embodiments of expansion of the high pressure air stream 40 to recover power. The embodiment shown in FIG. 5, would be used where there exists a source of suitable waste heat. In this embodiment, high pressure air stream 40 is heated in a recuperator 128 by waste heat from a gas turbine 129 (“GT Peaker”) that is used to supply power to generate additional electrical energy during peak demand times up to as high a temperature as possible to produce a heated air stream 130 that is expanded through expander 132. The exhaust 134 is reheated in recuperator 128 that is expanded in an expander 135 to produce an exhaust stream 136. As shown in FIG. 4, optionally, as the waste heat duty permits, the exhaust stream 136 can subsequently be reheated in recuperator 128 to produce a reheated stream 137 that can in turn be expanded in expander 138 to produce an exhaust stream 140. All of the aforesaid expanders are connected through a gear box 142, known in the art, to a generator 144 to generate electrical power. A part 146 of the exhaust stream 140 can be then directed toward the pre-purification unit 48 to regenerate adsorbents and discharge a stream 148 that would be rich in the higher boiling contaminants within the air, namely carbon monoxide, water vapor, carbon dioxide and other hydrocarbons. The remaining part 149 of the exhaust stream 140 is vented. As an alternative, an air stream could be withdrawn after entering the recuperator 128 to regenerate the adsorbent within the pre-purification unit 48. Among sources of waste heat the following should be noted: process heat from industrial processes, geothermal heat, and heat carried by solar thermal farm operating fluid; the combustion turbine flue gases represent the most practical source of waste heat for the application here envisioned. The exact number of reheats and expansion stages is determined by the amount of waste heat available and the desired conversion efficiency. For most situations, the number of expanders will range from 2 to 4.

In another embodiment shown in FIG. 6, there is no suitable source of waste heat present. In such embodiment, the high pressure air stream 40 is introduced into a recuperator 150 where it is reheated to produce a heated air stream 152 by the flue gases exiting a hot expander 154. The heated air stream 152 is then expanded through a warm expander 156, where it is expanded to produce an exhaust stream 160 that is at a pressure compatible with the operation of a combustor 162. It is to be noted that part of the exhaust stream 160 could be used to regenerate the adsorbent within the pre-purification unit 48. The air is mixed with a suitable fuel (preferably natural gas) and burned in combustor 162. The air enters the hot expander 154 with a turbine inlet temperature as high as compatible with the technology employed in the expander. It is here envisioned that the expander can tolerate a turbine inlet temperature of 1000° C. The air is then directed through the hot expander and expanded to a pressure close to atmospheric. The flue gases exiting the hot expander are directed toward the recuperator 150. A flue gas stream 168 is discharged from the recuperator 150 that is either vented to atmosphere, or processed in pollutants abatement systems to comply with emission requirements specific to the region of installation of the system. It is to be noted that the combustor 162 and the hot expander 154 could be used alone without the recuperator 150 or the warm expander 158.

It is to be noted that in any embodiment of the present invention, an atmospheric vaporizer could be used to vaporize part of the pumped liquid air stream 38 or to conduct such vaporization on an intermittent basis and then feed the resulting high pressure air to one or more expanders to recover power and generate electrical energy. Furthermore, although not illustrated, during the energy recovery phase, part of an expanded stream can be withdrawn and used to feed an industrial facility that can make use of a pressurized warm air stream. Such withdrawal can take place before, during, or after the air expansion has taken place.

Apparatus 1 can be started, when the regenerator 22 is no longer cold, by operating the compressors 12 and 14 processing enough air to feed the liquefier, and as little extra air as possible while maintaining conditions compatible with the operation of said compressors. The extra air will then be redirected toward the expanders 118 and 124 used during the power production phase. The air liquefied by the liquefier 20 is stored in the storage tank 32 and sent through the regenerator 22 during the power production phase, although at first it will be able to sustain operation for a shorter time than design. This will allow for a partial cool down of the regenerator 22. Once the peak period has passed, the storage phase can restart. During this second step of charging, the compressors 12 and 14 should be operated to provide enough air to feed the liquefier 20 and enough air to take advantage of the refrigeration stored in the regenerator 22, and as little extra air as possible. The extra air will be sent to the expanders 114 and 118. By operating the system in this way, more liquid air will be produced during the second cycle than during the first. Continuing to adopt this approach for a suitable number of cycles will allow the system to reach steady state operation without needing significant liquid addition from other sources.

Alternative ways of starting apparatus 1 can include proceeding in the manner outlined above, but not deploying the air in the regenerator 22 until enough air to supply a full day of operation is available in the tank or not deploying the air in the regenerator 22 until enough air to cool the entire regenerator 22 is available in the tank liquid storage tank 32. Other possibilities involve compressing enough air to feed the liquefier 20 and vent all the extra air or starting the apparatus 1 by liquid addition in the liquid storage tank 32.

Apparatus 1 can be operated so as to have a continuous storage phase of a duration compatible with the low price hours in a particular power market (typically ranging from 3 to 12 hours), and a power production phase of a duration compatible with the high price hours of said particular power market (typically ranging from 1 to 12 hours). In order to provide other types of services to the market, such as frequency regulation and ancillary services, spinning reserves, interruptible loads, and generation capacity, the system may be operated in an intermittent fashion, where less than a full load of air is stored before being deployed, and with said cycle being repeated several times a day. The specific mode of operation will be strongly influenced by the details of the power market which the system will be serving.

The following Table 1 summarizes the conditions of the main streams both during the storage and power producing phases in the embodiment of the present invention shown in FIG. 1. TABLE 1A and TABLE 1B show a summary of the conditions of the streams shown in FIG. 5 and FIG. 6, respectively. The flows are expressed in arbitrary units. Table 2 summarizes the power consumed and produced during the storage and power producing phases, respectively. The power consumption is expressed in kW per metric ton of inlet air (1). In order to obtain actual power consumptions in kW it is necessary to multiply said values by the flow rate of stream 1, expressed in metric tons per hour.

TABLE 1 Flow Pressure Stream Arbitrary Units Temperature K psia 10 1000 290 14.5 42 1000 302.5 101 18 747 302.5 2000 16b 505 302.5 2000 16a 111 302.5 2000 78 111 225 669 16c 252 220 1998 16d 252 220 1998 82 252 102 101 24 252 105 1997 24 after valve 27 252 80 17 26 747 103 1997 26 after subcooler 56 747 99 1996 and before valve 28 26 after valve 28 747 80 17 58 before subcooler 56 244 80 17 30 before valve 31 755 80 17 30 after valve 31 755 79 14.7 58 after subcooler 56 244 101 16.5 55 111 301 668 44 252 301 99 45 244 301 15 34 959 79 14.7 38 959 85 2000 40 959 280 1990

TABLE 1A 130 959 768 1987 134 959 517 413 134 prior to turbine 135 959 768 411 136 959 514 82 137 959 768 81 1490  815 504 16 148 144 504 15

TABLE 1B 152 959 557 1987 160 959 338 300 168 959 400 15

TABLE 2 Power Item kW/tph Feed Air compressor 12 −59 Recycle Compressor 14 −177 Liquefier Turbines (68, 70 and 72) 8.4 Pump 36 −5.6 (FIG. 5) Expanders 132, 135 and 138 212.9 (FIG. 6) Expander 156 55.9 (FIG. 6 Expander 154 188.9

Although the present invention has been described with reference to preferred embodiments, as would occur to those skilled in the art, numerous changes, additions could be made without departing from the spirit and scope of the invention as set forth in the appended claims. 

1. A liquid air storage and energy recovery method comprising: during an energy recovery phase, recovering energy from liquid air stored in a storage tank by pumping a stream of the liquid air to produce a pumped air stream, passing the pumped air stream through a regenerator such that refrigeration contained in the pumped air stream is stored within the regenerator and the pumped air stream warms within the regenerator to produce a pressurized air stream and expanding the pressurized air stream to produce power; during a liquid air storage phase, liquefying air to produce a liquid air stream and introducing the liquid air stream into the storage tank to produce the liquid air stored in the storage tank; and providing part of a refrigeration requirement for liquefying the air with the refrigeration stored in the regenerator, and providing another part of refrigeration by means of a liquefier.
 2. The liquid air storage and energy recovery method of claim 1, wherein: an air stream is compressed to produce a compressed air stream; a first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part by dividing the compressed air stream into two portions; the first subsidiary stream is introduced into the liquefier to produce a first cooled, high pressure air stream; the second subsidiary stream is introduced into the regenerator to produce a second cooled high cooled high pressure air stream; a vapor phase stream indirectly exchanges heat with the second cooled high pressure air stream to further cool the second cooled high pressure cooled high pressure air stream; the first and second high pressure air streams are expanded and introduced into a phase separator to produce a liquid phase and a vapor phase; the vapor phase stream is composed of the vapor phase and after the indirect exchange of the heat with the second high cooled high pressure air stream, the vapor phase stream is introduced into the liquefier and indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream; and the liquid air stream is composed of the liquid phase and is expanded to a lower pressure and introduced into the storage tank; whereby, the part of the refrigeration requirement for liquefying the air is provided by cooling the second subsidiary stream within the regenerator, indirectly exchanging heat from the second high pressure air stream to the vapor phase stream and the indirect heat exchange of the vapor phase stream within the liquefier.
 3. The liquid air storage and energy recovery method of claim 2, wherein: the air stream is compressed in a feed compressor along with a first recycle stream to form a first combined stream; the first combined stream is compressed in a recycle compressor along with a second recycle stream to form a second combined stream; the second combined stream is divided into the first subsidiary stream and the second subsidiary stream; the first subsidiary stream is expanded at two temperature levels within the liquefier to generate first and second exhaust streams that indirectly exchange heat with the air cooling within the liquefier; the first exhaust stream results from expansion at a lower of the two temperature levels and the second exhaust stream results from expansion at a higher of the two levels; the first exhaust stream forms the first recycle stream after having been fully warmed within the liquefier; and the second exhaust stream forms the second recycle stream after having been fully warmed within the liquefier.
 4. The method of claim 3, wherein the vapor phase stream after having exchanged heat with the air cooling within the liquefier is recycled back to the inlet of the feed compressor.
 5. The liquid air storage and energy recovery method of claim 1, wherein: the pressurized air stream is heated in a heat recuperator; and the pressurized air stream is expanded in at least two expanders, serially connected, with re-heat within the heat recuperator between the at least two expanders.
 6. The liquid air storage and energy recovery method of claim 5, wherein: the pressurized air stream is heated in a heat recuperator; and the pressurized air stream is expanded in at least two expanders, serially connected, with re-heat within the heat recuperator between the at least two expanders; a high temperature exhaust stream is produced as a result of the expansion of the pressurized air stream; the first combined stream is purified within a pre-purification unit; and adsorbent within the pre-purification unit is regenerated with the high temperature exhaust stream.
 7. The liquid air storage and energy recovery method of claim 1, wherein: the pressurized air stream is heated within a recuperator to form a heated stream; the heated stream is expanded in a first expander to produce a first exhaust stream; the first exhaust stream is introduced into a combustor to produce a flue gas stream; the flue gas stream is expanded in a second expander operating at a higher temperature than the first expander to produce a second exhaust stream; and the second exhaust stream is introduced into the recuperator to heat the pressurized air stream.
 8. The liquid air storage and energy recovery method of claim 1, wherein: an air stream is compressed to produce a compressed air stream; a first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part by dividing the compressed air stream into two portions; the first subsidiary stream is introduced into the liquefier to produce a first cooled high pressure air stream; the second subsidiary stream is introduced into the regenerator to produce a second cooled high pressure air stream; the first subsidiary air stream and the second subsidiary air stream are expanded and introduced into a phase separator to produce a liquid phase and a vapor phase; a vapor phase stream composed of the vapor phase is introduced into the liquefier and indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream; and the liquid air stream is composed of the liquid phase, is expanded to a lower pressure and introduced into the storage tank; whereby, the part of the refrigeration requirement for liquefying the air is provided by liquefying the second subsidiary stream within the regenerator and the indirect heat exchange of the vapor phase stream within the liquefier.
 9. The liquid air storage and energy recovery method of claim 2, wherein the vapor phase stream indirectly exchanges heat with the first cooled high pressure air stream and the second cooled high pressure air stream to subcool the first high pressure air stream and the second cooled high pressure air stream.
 10. The liquid air storage and energy recovery method of claim 1, wherein the pressurized air stream is expanded by introducing the pressurized air stream into a combustor and expanding resulting flue gases in an expander.
 11. The liquid air storage and energy recovery method of claim 1, wherein at least air that is introduced into the liquefier is purified of higher boiling contaminants comprising hydrocarbons, carbon dioxide and water vapor.
 12. The method of claim 2 or claim 3, wherein the air stream is compressed to a supercritical pressure and the stream of the liquid air is pumped to a supercritical pressure.
 13. A regenerator comprising two or more pipe bundles, said bundles connected to each other through one or more conduits with a higher thermal resistance than the thermal resistance of each bundle as a whole so that heat will not be conducted through the one or more conduits between bundles, the pipe bundles being located within a thermal storage medium.
 14. The regenerator of claim 13, wherein the thermal storage medium is water, and the pipe bundles are submerged within a pool of the water either in solid or liquid form.
 15. The regenerator of claim 13, where each pipe bundle is embedded in a thermal storage medium, the thermal storage medium is composed of a mixture of substances that will change phase during the storage and production phases.
 16. The regenerator of claim 13, wherein the thermal storage medium is cement, gravel, ceramic, or a mineral matrix.
 17. A liquid air storage and energy recovery apparatus comprising: a storage tank for storing liquid air; a pump connected to the storage tank to pump a stream of the liquid air during an energy recovery phase of operation, thereby to produce a pumped liquid air stream; a regenerator connected to the pump, the regenerator configured such that refrigeration contained in the pumped liquid air stream is stored within the regenerator and the pumped liquid air stream vaporizes within the regenerator to produce a pressurized air stream; at least one expansion device connected to the regenerator configured to expand the pressurized air stream and thereby to produce power; a liquefier integrated with the regenerator such that during a liquid air storage phase, an air stream is liquefied to produce a liquid air stream through the refrigeration stored in the regenerator during the energy recovery phase and additional refrigeration produced by the liquefier; and the storage tank in flow communication with the liquefier and the regenerator such that the liquid air stream is introduced into the storage tank to produce the liquid air stored in the storage tank.
 18. The liquid air storage and energy recovery apparatus of claim 17, wherein: at least one compressor compresses an air stream and thereby produces a compressed air stream; the liquefier and the regenerator are in flow communication with the at least one compressor such that a first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part from the compressed air stream, the first subsidiary compressed stream is introduced into the liquefier to produce a first cooled high pressure air stream and the second subsidiary stream is introduced into the regenerator to produce a second cooled high pressure air stream; two expansion valves are positioned between the regenerator and the liquefier and a phase separator such that the first cooled high pressure air stream and the second cooled high pressure air stream are expanded and introduced into the phase separator to produce a liquid phase and a vapor phase; a heat exchanger is positioned between the phase separator and the liquefier and is configured such that a vapor phase stream composed of the vapor phase indirectly exchanges heat with the second cooled high pressure air stream to subcool the second cooled high pressure air stream and the vapor phase stream is introduced into the liquefier; the liquefier is configured such that the vapor phase stream indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream; and the storage tank is in flow communication with the phase separator and another expansion valve is positioned between the phase separator and the storage tank such that a liquid air stream, composed of the liquid phase, is expanded to a lower pressure and introduced into the storage tank; whereby, the part of the refrigeration requirement for liquefying the air is provided by liquefying the second subsidiary stream within the regenerator, indirectly exchanging heat from the second cooled high pressure air stream to the vapor phase stream and the indirectly heat exchange of the vapor phase stream within the liquefier.
 19. The liquid air storage and energy recovery apparatus of claim 18, wherein: the at least one compressor comprises a feed compressor and a recycle compressor, the feed compressor compressing the air stream along with a first recycle stream to form a first combined stream and the recycle compressor connected to the feed compressor such that the first combined stream is compressed along with a second recycle stream to form a second combined stream; the liquefier and the regenerator are connected to the recycle compressor so that the second combined stream is divided into the first subsidiary stream and the second subsidiary stream; the liquefier has two expanders positioned at two temperatures levels within the liquefier such that the first subsidiary stream is expanded at two temperature levels within the liquefier to generate first and second exhaust streams, the first exhaust stream resulting from expansion at a lower of the two temperature levels and the second exhaust stream resulting from expansion at a higher of the two levels and a heat exchange network positioned within the liquefier such that the first and second exhaust streams indirectly exchange heat with the air cooling within the liquefier; the feed compressor is connected to the liquefier so that the first exhaust stream forms the first recycle stream after having been fully warmed within the liquefier; and the recycle compressor is connected to the liquefier so that second exhaust stream forms the second recycle stream after having been fully warmed within the liquefier.
 20. The liquid air storage and energy recovery apparatus of claim 18, wherein the liquefier is connected to the feed compressor such that the vapor phase stream is recycled back to the inlet of the feed compressor.
 21. The liquid air storage and energy recovery apparatus of claim 17, wherein: the at least one expansion device comprises at least two expanders, serially connected, to expand the pressurized air stream; and a heat recuperator positioned between the at least two expanders to reheat the pressurized air stream.
 22. The liquid air storage and energy recovery method of claim 21, wherein: the at least two expanders produce a heated exhaust stream; a pre-purification unit having an adsorbent purifies air of contaminants; the pre-purification is positioned between the feed compressor and the recycle compressor so that the first combined stream is purified within the pre-purification unit; and the pre-purification unit is connected to the at least two expanders to receive a part of the heated exhaust stream to regenerate adsorbent within the pre-purification unit.
 23. The liquid air storage and energy recovery apparatus of claim 17, wherein: The at least one expansion device is a first expander and a second expander; a recuperator heats the pressurized air stream and thereby to form a heated stream; the first expander is connected to the recuperator to expand the heated stream and thereby to produce a first exhaust stream; a combustor is connected to the first expander to expand the first exhaust stream and thereby to produce a flue gas stream; the second expander is connected to the combustor to expand the flue gas stream at a higher temperature than the first expander to produce a second exhaust stream; and the recuperator is also connected to the second expander so that the second exhaust stream is introduced into the recuperator to heat the pressurized air stream.
 24. The liquid air storage and energy recovery apparatus of claim 17, wherein: at least one compressor compresses an air stream and thereby produces a compressed air stream; the liquefier and the regenerator are in flow communication with the at least one compressor such that a first subsidiary compressed stream and a second subsidiary compressed stream are formed at least in part from the compressed air stream, the first subsidiary compressed stream is introduced into the liquefier to produce a first cooled high pressure air stream and the second subsidiary stream is introduced into the regenerator to produce a second cooled high pressure air stream; two expansion valves are positioned between the regenerator and the liquefier and a phase separator such that the first cooled high pressure air stream and the second cooled high pressure air stream are expanded and introduced into the phase separator to produce a liquid phase and a vapor phase; the liquefier is connected to the phase separator and is configured such that a vapor phase stream composed of the vapor phase indirectly exchanges heat with the air cooling within the liquefier that forms the first cooled high pressure air stream; and the storage tank in flow communication with the phase separator and another expansion valve positioned between the phase separator and the storage tank such that a liquid air stream, composed of the liquid phase, is expanded to a lower pressure and introduced into the storage tank; the liquid air stream is composed of the liquid phase, is expanded to a lower pressure and introduced into the storage tank; whereby, the part of the refrigeration requirement for liquefying the air is provided by liquefying the second subsidiary stream within the regenerator and the indirect heat exchange of the vapor phase stream within the liquefier.
 25. The liquid air storage and energy recovery apparatus of claim 18, wherein the heat exchanger is also configured such that the vapor phase stream also indirectly exchanges heat with the first cooled high pressure air stream to subcool the first cooled high pressure air stream.
 26. The liquid air storage and energy recovery apparatus of claim 17, wherein a combustor is positioned between the at least one expansion device and the regenerator such that the pressurized air stream supports combustion within the combustor to generate a flue gas stream and the flue gas stream is expanded within the at least one expansion device.
 27. The liquid air storage and energy recovery apparatus of claim 18, further comprising a pre-purification unit containing molecular sieve adsorbent, the pre-purification unit is connected to the at least one compressor so that at least part of the compressed air is purified within the pre-purification unit. 